The sample holder is a component of an electron microscope providing the physical support for samples under observation. Sample holders traditionally used for TEMs and STEMs, as well as some modern SEMs, consist of a rod that is comprised of three key regions: the end, the barrel and the specimen tip. In addition to supporting the sample, the sample holder provides an interface between the inside of the instrument (i.e., a vacuum environment) and the outside world.
To use the sample holder, one or more samples are first placed on a sample support device, e.g., a MEMS device. The sample support device is then mechanically fixed in place at the specimen tip, and the sample holder is inserted into the electron microscope through a load-lock. During insertion, the sample holder is pushed into the electron microscope, assisted by the vacuum within the microscope, until it stops, which results in the specimen tip of the sample holder being located in the column of the microscope. At this point, the barrel of the sample holder bridges the space between the inside of the microscope and the outside of the load lock, and the end of the sample holder is outside the microscope. To maintain an ultra-high vacuum environment inside the electron microscope, flexible O-rings are typically found along the barrel of the sample holder, and these O-rings seal against the microscope when the sample holder is inserted. The exact shape and size of the sample holder varies with the type and manufacturer of the electron microscope, but each holder contains the three aforementioned key regions.
Some sample holders can be used to provide a means for gas or liquid to flow into and out of a cavity at the specimen tip of the holder. To establish temporary or continuous flow of liquid or gas, a pump located external to the sample holder can be used to force liquids into a cavity at the specimen tip of the holder. The pumping equipment is typically outside of the holder, and various connectors are used to bring the liquid or gas to the sample holder, down the length of the holder, to the cavity at the tip of the holder and back out. Use of a pump to flow the liquid is typical, but any method of creating a pressure differential could be used to establish flow. For example, a pressurized reservoir on the entry port or a depressurized reservoir on the exit port(s) would also establish flow.
One type of sample support device is an environmental cell in which (1) two semiconductor devices, i.e., MEMS devices, comprising thin windows can be placed, (2) specimens can be placed on or near the semiconductor devices and (3) using the combination of holder and devices, wherein the specimen's environment, including an electrical field and a gas or liquid flow, can be precisely controlled. The present inventors previously described novel apparatuses and methods to contact and align devices used to form liquid or gas cells in International Patent Application No. PCT/US2011/46282 filed on Aug. 2, 2011 entitled “ELECTRON MICROSCOPE SAMPLE HOLDER FOR FORMING A GAS OR LIQUID CELL WITH TWO SEMICONDUCTOR DEVICES,” which is hereby incorporated herein in its entirety.
The tubing that is used to deliver liquid and/or gas to the tip of the holder will typically be a relatively small tubing with a small inner diameter, such as 200 microns or less. The benefit of using small inner diameters include: minimizing the volume of fluid in the lines in the event of a leak inside the microscope column. Less fluid will theoretically cause less fluid to escape into the microscope column; and reducing the amount of time required to move fluid from the source to the tip of sample area of the holder. For example, if there were to be 100 micro-liters of fluid in the inlet line, a flow rate of 100 micro-liters per hour would require 60 minutes to introduce a fluid to the sample area. Disadvantages of using such small tubing diameters include the tubing can easily become clogged, either through precipitation or trapped particles. This will require user intervention at best and repair of the holder at worse; and the tubing is more difficult to clean because it is limited to flushing as the small size does not easily permit a means to clean with a physical tool.
It would be advantageous to be able to insert and remove temporary fluidic pathways, sensors or other tools without the need to dissemble the holder. Affixing (i.e., sealing) these types of sensors and other tools in place limits the ability to repair or replace them or move them to a different position. However, if larger, pathways or capillaries could be used, there would exist an ideal route to deliver replaceable fluidic pathways (i.e., a tube-within-a-tube design), sensors and other tools to within close proximity of the sample area to measure or apply stimulus to the sample and/or surrounding fluid.
Accordingly, there exists a need in the art for a sample holder that can overcome the aforementioned disadvantages. Towards that end, an apparatus and method is disclosed herein that enables insertion and retraction of modular components within an environmental electron microscope holder. By not requiring disassembly of the sample holder, the vacuum and dimensional specifications of the apparatus can be maintained.